Even in Japan only, tens of thousands of fires occurs every year. Therefore, a fire is a serious problem for the global environment and human society. When a fire breaks out, it is important to efficiently extinguish the fire in order to minimize damage. As a conventional extinguishing agent, water and an aqueous extinguishing agent have been used. As a general aqueous extinguishing agent, APC extinguishing agent mainly consisting of potassium carbonate aqueous solution is known. Such APC extinguishing agent contains a synthetic surfactant in order to lower the surface tension thereof and improve wetting property and permitting property to a combustible material such as woods, fiber and resin. In addition, adhesive property is improved, since APC extinguishing agent is foamed by a synthetic surfactant. Due to the above properties, fire extinguishing effect, reheat-prevention effect and fire spread-prevention effect are improved, and it is known that APC extinguishing agent can extinguish a fire in a shorter time and in a smaller amount than water alone.
However, even for the above-described fire-extinguishing performance, low safety of a conventional extinguish agent for the environment and human body is acknowledged as a problem.
For example, though APC extinguishing agent is particularly effective in extinguishing a fire caused due to cooking oil having high temperature, the agent shows strong basicity and the pH thereof is 12 to 13. Therefore, furniture, eating utensils, a device and the like to which the agent adheres should be thoroughly washed or discarded. In addition, a metallic structural body, metallic fittings or the like do not burn but may possibly become eroded by APC extinguishing agent. Furthermore, when a conventional extinguishing agent which contains a synthetic surfactant is sprayed, a secondary damage after fire extinguishment is caused. For example, such an extinguishing agent is highly toxic to an aquatic organism.
Under the above-described circumstances, an extinguishing agent which contains a natural surfactant, such as lecithin, saponin and casein, was recently developed in order to reduce pressure on the environment or human body (Patent Document 1).